Liquid guns, modules and dispensers are routinely used to dispense viscous liquids, such as hot melt adhesives, sealants and other thermoplastic materials, in a variety of dispensing applications employed in the manufacture of products and in product packaging. The flow and discharge of liquid in conventional liquid dispensers is regulated by either a pneumatically-actuated valve assembly or an electrically-operated valve assembly. Generally, valve assemblies of liquid dispensers feature a valve element movable for selectively contacting a valve seat to provide distinct opened and closed conditions that permit and interrupt, respectively, the flow of liquid to a dispensing orifice. Hence, cyclic movement between the opened and closed positions causes intermittent flow discontinuities required to generate a pattern of liquid on a surface of the product or product packaging.
Conventional electrically-operated liquid dispensers include a stationary pole, a movable armature coupled with the valve element, and an electromagnetic coil that causes the armature to move relative to the pole for providing the opened and closed conditions. The armature and pole are typically cylindrical components located inside the inner diameter of the solenoidal windings of the electromagnetic coil and that adjoin at an interface inside the inner diameter. As a result, the windings are constrained by, and must conform to, the circular cross-sectional profile of the armature and pole. The conventional arrangement of the pole, armature and electromagnetic coil inside the liquid dispenser does not make efficient use of the open space available inside the dispenser's body. As a result, the spacing between adjacent electrically-operated liquid dispensers cannot be sufficiently reduced, which is detrimental for some small footprint applications applying closely-spaced amounts of liquid on the surface of the product or product packaging. Changing the shape of the liquid dispenser's body from a cylindrical object to a parallelepiped may permit denser packing of adjacent dispensers. However, merely packaging the concentric pole and coil inside a rectangular or trapezoidal dispenser body does not cure the limitations for spacing adjacent conventional liquid dispensers as the cylindrical coil geometry provides a fundamental limitation on the shape and dimensions of the body.
Conventional electrically-operated liquid dispensers suffer from additional deficiencies. One such deficiency is the size of the armature, which is immersed in the dispensed fluid. The inertia and resistance supplied by the dispensed liquid that must be overcome to initiate and sustain movement increases commensurate with the increases in the size of the armature. The field lines cross an air gap present at an interface between confronting surfaces of the pole and the armature. In addition, the field lines must cross a side air gap between a sidewall of the armature and a surrounding magnetic member that guides the field lines into the sidewall of the armature. The additional magnetic member and this side air gap are necessary for creating a closed flux path. The existence of this side air gap increases the reluctance and, hence, reduces the magnetic efficiency of the liquid dispenser. Furthermore, the mass of armature is increased as the armature must be sized to permit a closed flux path that contains both the side air gap between the armature and the magnetic member and the air gap between the confronting surfaces of the pole and armature.
It would therefore be desirable to provide an electrically-operated liquid dispenser having a compact, space-efficient pole design that is likewise magnetically efficient.